Organic Light Emitting Diode (OLED) displays are known in the art. These displays are typically formed from a two-dimensional array of light emitting OLEDs. These solid-state emissive displays typically provide a high contrast ratio for static and dynamic patterns and wide viewing angle, thus providing a very high quality two-dimensional image.
Stereoscopic displays are also known in the art. These displays may be formed using a number of techniques; including barrier screens such as discussed by Montgomery in U.S. Pat. No. 6,459,532 and optical elements such as lenticular lenses as discussed by Tutt et al in U.S. Patent Application 2002/0075566. Each of these techniques concentrates the light from the display into a narrow viewing angle, providing an auto-stereoscopic image. Unfortunately, these techniques typically reduce the perceived spatial resolution of the display since half of the columns in the display are used to display an image to either the right or left eye. These displays also reduce the viewing angle of the display, reducing the ability for multiple users to share and discuss the stereoscopic image that is being shown on the display.
Among the most commercially successful stereoscopic displays to date have been displays that either employed some method of shuttering light such that the light from one frame of data is able to enter only the left or right eye and left and right eye images are shown in rapid succession. Two methods have been employed in this domain; including displays that employ active shutter glasses or passive polarizing glasses. Systems employing shutter glasses display either a right or left eye image while an observer wears active LCD shutters that allow the light from the display to pass to only the appropriate eye. While this technique has the advantage that it allows a user to see the full resolution of the display and allow the user to switch from a monoscopic to a stereoscopic viewing mode, the update rate of the display is typically on the order of 120 Hz, providing a 60 Hz image to each eye. At this relatively low refresh rate, most observers will experience flicker resulting in significant discomfort if the display is used for more than a few minutes within a single viewing session. Even when the display is refreshed at significantly higher rates, flicker is often visible when the display is large and/or high in luminance.
Displays employing polarization have also been discussed and employed. For example, Wolk et al in U.S. Pat. No. 6,485,884 has discussed the design and manufacture of an OLED display that emits linear polarized light and that can be used to provide a stereoscopic display. Using this approach, the organic materials are oriented when patterned onto the substrate such that they emit linearly polarized light. When these materials are patterned such that alternating columns have different linear polarizations and the observer wears glasses in which each lens has a different linear polarization, each eye sees the light from alternating columns in the display. Using this display, a stereoscopic image can be displayed with every other column of pixels from the left and right eye images being displayed on alternating columns of the display. While this method provides a stereoscopic image, the resulting stereoscopic image has half the spatial resolution of display. Since the polarization is permanently fixed during the manufacture of the display, alternating columns on this display always have different polarizations and alternating columns will vary significantly in appearance when the display is viewed without polarized glasses that provide the stereoscopic effect, making the display of little use when viewed without appropriately polarized glasses. Further, it is well known that stereoscopic displays formed using linear polarization suffer from a number of artifacts; including narrowing of display's viewing angle and cross-talk (i.e., leakage of light intended for one eye to the other eye) when the linear polarized glasses are turned to an angle other than perpendicular to the columns of the display.
It is known in the art that displays employing circularly polarized light provide many advantages over displays that employ linear polarized displays. Specifically, these displays do not suffer from significantly increased cross-talk when the observer tilts his or her head. These displays typically provide a linear polarizing layer, a quarter-wave plate to create circularly polarized light, and a switchable or patterned half-wave plate to rotate the handedness of the polarization for half of the image. Byatt, 1981 (U.S. Pat. No. 4,281,341) has described a system employing a switchable polarizer that is placed in front of a CRT and performs very similarly to shutter glasses, using the polarization to select which eye will see each image. This system has the advantage over shutter glasses that the user does not need to wear active glasses, but otherwise suffers from the same deficiencies, including flicker.
Lipton, 1985 (U.S. Pat. No. 4,523,226) described a display system that will not suffer from flicker, but instead uses two separate video displays and optics to present the images from the two screens appropriately for the two eyes. While this display system does not suffer from the same visual artifacts as the system employing switchable polarization that was described by Byatt, the system requires two separate visual displays and additional optics, providing increasing the cost of such a system.
Circular polarization has also been used in systems to provide lower resolution images without flicker, using an approach that is similar to that employed in barrier screen displays. Lipton 1997 (U.S. Pat. No. 5,686,975) and Ma, 2000 (U.S. Pat. No. 6,020,941) each describe display systems where alternating columns of a display device are each provided with circular polarizers that are arranged in columns, such that alternating columns provide light that is circularly polarized with left and right handed orientation. By changing the handedness of the polarization in this way, and by wearing polarized glasses, each eye is provided alternating columns of the information from the display. However, as the handedness of the polarization of the light is kept constant during display of stereoscopic imagery, the resolution is reduced due to the fact that each eye can only see half of the columns of the display while viewing stereoscopic imagery. Faris, 1998 (U.S. Pat. No. 5,844,717) and Faris, 2002 (U.S. Pat. No. 6,359,664) have described similar displays that provide stereoscopic images by arranging a two-dimensional array of micropolarizers on a display surface with each eye being able to see a checkerboard pattern of the image. These micropolarizers are static and therefore each of the observers' eyes once again see only half the resolution of the display. It is notable, that since each eye sees only half the area of the display, the perceived brightness of the display is also reduced by a factor of two. These polarized displays suffer from one additional constraint due to the fact that the transmission of the polarizing layer is wavelength dependent. Because of this effect, the color purity of the display and often the viewing angle is reduced by the presence of the polarizer as different colored pixels of light pass through a single polarizer that has not been optimized to transmit the luminance at the center wavelength of the emitted light.
Kalmanash in U.S. Pat. No. 4,877,307 discussed the wavelength sensitivity of the circular polarizing layer and proposed a CRT with three sheets of circular polarizers that are stacked between a linear polarizing layer and an active retarder for manipulating the handedness of the polarization. In this display device, each of the circular polarizing layers are composed of materials having a center wavelength that is matched to the peak wavelength of the red, green, and blue emitters in the display device. This stack of three circular polarizing layers was proposed to improve the circular polarization of the colored light from the three-color display. Unfortunately, Kalmanash does not address the problem that each of the circular polarizers can affect polarization over a range of wavelengths and therefore the circular polarizers at the top of the stack may interfere with and, for some wavelengths of the light, will reduce the circular polarization that is introduced by the circular polarizers at the bottom of the stack. Kalmanash also fails to solve the problem that the active half-wave retarded that is used to rotate the handedness of the circular polarization is also highly wavelength dependent and is therefore incapable of fully changing the handedness of circular polarized light that includes a broad range of wavelengths with multiple peaks as is common within a color imaging device.